Stiffening sheet material



iatented Sept. 26, 1939 UNITED STATES PATENT OFFICE 2,173,861 STIFFENING SHEET MATERIAL Jersey No Drawing. Application May 5, 1936, Serial No. 77,917

9 Claims.

This invention relates to the impregnation of a fabric with a derivative of cellulose by precipitating the latter in a highly porous form in and on the fabric to form a. stiffening material.

An object of the invention is the economic production of a stiffening material that is readily and uniformly attacked by the liquids that render t-he'matcrial fiaccio and adhesive. Other objects of the invention will appear from the following detailed description.

Although this invention is applicable to the production of stiffening material which is useful for many purposes, it will be described in particular with the manufacture of box toes and counters for shoes. The manufacture of box toes or shoe stiffeners is generally carried out by precipitating a cellulose derivative in the form of fine particles in the interstices of a cloth. After the cloth has been impregnated and allowed to dry, blanks of convenient shape and size are cut out by the manufacturer. These blanks are then dipped for a very short time in a solvent bath whose strength is carefully regulated to impart the desired degree of gelatinization and pliability. While in a flaccid and swollen condition, due to the effect of the solvent bath thereon, the box toes are cemented or laminated between the inner cloth lining and the outside leather layer. The

reinforced composite is then shaped over a wooden last to the contour of the shoe and the solvent allowed to volatilize to produce a stiffened form.

It has been customary in forming this fabric, first to impregnate the fabric skeleton with a derivative of cellulose and then immediately pass it into a precipitating bath. The precipitation which at first is a mere surface condition, gradually penetrates throughout the shaped material. Another way of forming this material was to first impregnate the fabric skeleton with a derivative of cellulose in a volatile solvent and thenallow the same to dry in contact with the air. Both of these methods, however, produced a surface condition which prevented the attack of solvents when the material is treated therewith to make the material flaccid for use in the lasting operation. stiffening material made by the prior methods resulted in a very ununiform adhesion between the said stiffening material and the layers of sheet material and also resulted in a material having ununiform degrees of pliability. By prior methods an article of poor shape and quality was produced. I have now found that if the derivative of cellulose is deposited in and on the fabric skeleton in such a manner that the same is uniformly and highly porous throughout, w thout an inner colloidal core or an outer skin, the stiffening fabric-may be softened by a softening fluid readily and uniformly.

Another disadvantage found in the stiffening materials produced prior to this invention was that when the stiffening material was placed in a solvent for the cellulose derivative to make the stiffening material flaccid, the solvent attacked one part of the material more readily than other parts. It being necessary that all the material be softened by the solvent, those parts first attacked were often dissolved away before other parts of the base material were softened. I have found that by precipitating the material in a fabric skeleton in accordance with my invention, all parts of the cellulose derivative are attacked by the softening solution with equal speed. The derivative of cellulose on the interior of the material prepared in accordance with this invention is attacked with the same speed as the cellulose derivative on the surface. Consequently,

entire sheet without dissolving any of the derivative of cellulose from the fabric permits a longer use 'of the softening solution. Furthermore, there is no waste of the derivative of cellulose and all that was originally placed upon the fabric is to be found in the finished article.

A further advantage of the material made in accordance with my invention is that the same becomes very adhesive and, in the manufacture of shoes the inner cloth liner and the outer leather cloth, are held firmly to the softened stiffening material so that they do not separate on being thrown into conveyor baskets or during handling while placing the same on lasts and like operations.

In accordance with my invention, I impregnate a base material with a derivative of cellulose by passing the base material through a solution or dope containing a derivative of cellulose, such ascellulose nitrate or cellulose acetate, with or without the addition of plasticizers, fire retardants, etc., scraping off the excess dope, and then precipitating the derivative of cellulose in and on the base material in such a manner that no colloidal core or skin is formed by the derivative of cellulose. The precipitation of the cellulose derivative in and on the base material is 'performed by subjecting the impregnated base material with a heated vapor of a precipitating ing a non-solvent vapor as a means of precipitating the derivative of cellulose in and on the base material, precipitation is caused to take place simultaneously throughout the thickness of the material. By employing the non-solvent vapor in the heated state the precipitation throughout the base material is substantially instantaneous, thus preventing by the speed of precipitation the formation of the agglomerates that tend to form colloidal cores and surface skins. The speedy precipitation produces a very porous and uniform condition of the derivative of cellulose.

This invention is applicable to the formation of stiffening material containing any suitable base, such as fabric, felt, leather, paper or other porous materials. In the formation of box toes and counters for shoes, it is preferable to employ as the base material a double napped flannel or villous fabric. The derivative of cellulose precipitated in and on the base material may be any suitable derivative of cellulose that is soluble in relatively low boiling solvents. Examples of such derivatives of cellulose are cellulose nitrate (of any suitable degree of nitration), organic esters of cellulose, examples of which are cellulose acetate, cellulose formate, cellulose butyrate and cellulose propionate, and cellulose others examples of which are 'ethyl cellulose, methyl cellulose and benzyl cellulose. Mixed ethers and esters may also be employed, such as cellulose aceto butyrate.

The derivative of cellulose may be applied to the base material in any suitable manner, such as by padding, spraying or other methods of applying a solution to a fabric. It is preferable, however, to apply the same by dipping the base material into a solution of the derivative of cellulose in a relatively low boiling solvent. After the fabric or other base material has been impregnated with a solution of the derivative of cellulose in a volatile solvent, precipitation is caused by a simultaneous removal of a part of the volatile solvent and the addition of a non-solvent. This may be accomplished by the use of live steam which not only removes, due to its temperature, the volatile solvent but also adds through condensation a precipitant for the derivative of cellulose. Although live steam is preferred due to its ready availability and cheapness, other vapors which are non-solvents for the derivatives of cellulose may be employed,

In a preferred form of my invention, the coating operation comprises briefly the passing of a double napped flannel fabric through a solution or dope of a derivative of cellulose, such as cellulose nitrate or cellulose acetate, with or without the addition of a plasticizer and/or fire retardant, scraping off the excess dope and speedily precipitating uniformly throughout the impregnated material the derivative of cellulose in and on the fibres of the fabric and drying the resultant product. The impregnating solution or dope may be made to contain any suitable concentration of the derivative of cellulose. The derivative of cellulose may be formed into the impregnating solution or dope by dissolving the same in a relatively low boiling solvent, such as acetone, methyl acetone, ethyl alcohol, methyl alcohol, etc., which may readily be flashed off from the dope or solution by the action of heat. Owing to the nature of the majority of solvents reclaiming systems it is preferable to use a water-soluble solvent. This is especially true when steam is applied as an aid in precipitating the derivative of cellulose.

In order to retard the flammability of the stiffening material containing cellulose nitrate or cellulose acetate compositions, any suitable quantity of fire retardants, such as' hydrated calcium sulphate, ammonium phosphate, cerium oxalate, calcium tartrate, etc. with or without phosphate acid esters, such as tricresyl phosphate, triphenyl phosphate etc., may be added.

When rigid or stiff box toe materials are desired, small amounts or no plasticizers are used, but when a less brittle or more yielding product is wanted varying amounts, but much less than 25 parts of of plasticizer by weight of the derivative of cellulose, may be employed. The plasticizers employed may be any of the nitrocellulose or cellulose acetate plasticizers well known in the art, such as camphor, triacetin, dimethyl phthalate, dimethoxy ethyl phthalate, paratoluol ethyl sulphonamide, dibutyl tartrate, tricresyl phosphate, etc.

As an aid in describing this invention, but without being limited thereto. the following examples of suitable impregnating solutions are given.

Example I Parts by weight Cellulose acetate 100 Dimethyl phthalate 10 Acetone 3'75 Example II Cellulose acetate 100 Acetone 400 Example III Cellulose acetate 100 Grain alcohol 400 Ethyl acetate 300 The solution in Formula III must be made in the warm between 60 and 70 C. It must also be applied warm. Precipitation may be induced when using this formula by cooling as well as by steam injection.

Example IV Parts by 1 weight Cellulose nitrate (ordinary commercial cellulose nitrate such as used in making film) 100 Acetone 400 Example V Cellulose nitrate (containing 10 parts of camphor) 100 Acetone 390 The above nitrocellulose impregnating solutions are preferably heated to a temperature of 110 to 115 F. during the impregnation of the fabric.

In any of the above impregnating solutions the cloth or base material may be passed through the same at any desired rate depending upon the amount and type of impregnation desired. For box toe materials for the manufacture of shoes, it is preferable to pass a double napped flannel cloth through the above solutions at a rate of about 5 or more feet per minute, The base material employed for the formation of box toe materials is preferably a double napped flannel which may vary in weight from 12 to 14 ounces or more per yard. The amount of precipitate in and on the fabric may also vary to some extent. The quantity of deposit in and on the base material may be regulated to a large extent by adjusting the spacing of the scraping knives between which the base material passes after being impregnated. Other methods of regulating the quantity of deposit may be employed, such as the concentration of the dope or impregnating solution, the speed of travel of the fabric through said solution, etc.

It is to be understood that this invention is not limited to the formation of stiffening material or box toes, but may be employed for many other uses. For other uses and even in some cases for box toes, the type of fabric specified above need not be employed. Instead any suitable type of fabric or other porous base material may be substituted therefor. Examples of other suitable fabrics are cotton muslin, plushes, velvets made of silk, wool or cotton, etc.

After the base material has been impregnated with the impregnating solution or dope the same is subjected to the action of the vapor of a nonsolvent. This may be accomplished by passing the impregnated base material through a steam chest wherein the impregnated base material is subjected to the action of steam and the heat contained by the steam in such a manner that the volatile solvent is speedily driven from the material and in such a manner that some of the steam condenses in and on the base material. In like manner the impregnated base material may be passed through chambers which contain vapors of other non-solvent liquids. In a preferred form of my invention, the action of the steam upon the impregnated base material is hastened by injecting the same into the impregnated base material. This is accomplished by passing the impregnated base material between jets from which steam is emitted under pressure. The jets are so formed that the steam is directed into the base material. By this latter method it is possible to simultaneously raise the entire thickness of the impregnated base material to a temperature sufficient to volatilize the solvent.

After the derivative of cellulose has been precipitated in and on the base material the same may be subjected to a drying operation in which the residual solvent and condensed non-solvent vapors are removed. The drying operation may be accomplished by passing the shaped material over a heated roll or drum. Other methods of drying the material may be employed, such as by passing the same through a heated chamber or leaving the same exposed to a drying atmosphere.

It is to be understood that the foregoing detailed description is given merely by way of iilustration and that many variations may be made therein, without departing from the spirit of my invention.

Having described my invention, what I desire to secure by Letters Patent is:

1. The process of manufacturing a sheet material capable of being made adhesive, flaccid, shaped and stiffened, which comprises preparing a solution of a derivative of cellulose in a low boiling solvent, impregnating a base sheet material with said solution and thereafter speedily precipitating thederivative of cellulose by applying a heated vapor of a precipitating agent to the impregnated sheet material.

2. The process of manufacturing a sheet material capable of being made adhesive, flaccid, shaped and stiffened, which comprises preparing a solution of cellulose nitrate in a low boiling solvent, impregnating a base sheet material with said solution and thereafter speedily precipitating the cellulose nitrate by applying a heated vapor of a precipitating agent to the impregnated sheet material.

3. The process of manufacturing a sheet material capable of being made adhesive, flaccid, shaped and stiffened, which comprises preparing a solution of cellulose acetate in a low boiling solvent, impregnating a base sheet material with said solution and thereafter speedily precipitating the cellulose acetate by applying a heated vapor of a precipitating agent to the impregnated sheet material.

4. The process of manufacturing a sheet material capable of being made adhesive, flaccid, shaped and stiffened, which comprises preparing a solution of a derivative of cellulose in a low boiling solvent, impregnating a base sheet material with said solution and thereafter speedily precipitating the derivative of cellulose by passing the sheet material through a steam bath.

5. The process of preparing a sheet material capable of being made adhesive, flaccid, shaped and stiffened, which comprises preparing a solution of cellulose nitrate in a low boiling solvent, impregnating a base sheet material with said solution and thereafter speedily precipitating the cellulose nitrate by passing the sheet material through a steam bath.

6. The process of manufacturing a sheet material capable of being made adhesivejflaccid, shaped and stiffened, which comprises preparing a solution of cellulose acetate in a low boiling solvent, impregnating a base sheet material with said solution and thereafter speedily precipitating the cellulose acetate by passing the sheet material through a steam bath.

7. The process of manufacturing a sheet material capable of being made adhesive, flaccid, shaped and stiffened, which comprises preparing a solution of a derivative of cellulose in a low boiling solvent, impregnating a base sheet material with said solution and thereafter speedily precipitating the derivative of cellulose by injecting steam into the impregnated sheet material.

8. The process of manufacturing a sheet material capable of being made adhesive, flaccid, shaped and stiffened, which comprises preparing a solution of cellulose nitrate in a low boiling solvent, impregnating a base sheet material with said solution and thereafter speedily precipitating the cellulose nitrate by injecting steam into the impregnated sheet material.

9. The process of manufacturing a sheet material capable of being made adhesive, flaccid, shaped and stiffened, which comprises preparing a solution of cellulose acetate in a low boiling solvent, impregnating a base sheet material with said solution and thereafter speedily precipitating the cellulose acetate by injecting steam into the impregnated sheet material.

ROY STAFFORD RITCHIE.

"4' I CERTIFICA'IE OF CORRECTION. Patent No. 2,175,861.

September 26, 1959. ROY STAFFORD RITCHIE.

It is hereby certified that error appeare in the printed specification of :the above numbered patent requiring correction as follows: Page 2, seco'nd column, line 73, for the word "some" read the same; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed-this 2mm day of October, A D. 19 9.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patent.v 

